Typically, when constructed, an offshore platform has the jacket legs, pile sleeves, and conductor pipes sealed to prevent water leakage therein to facilitate towing operations and platform installation. With the jacket legs, pile sleeves, and conductor pipes sealed against water leakage, the offshore platform is usually placed on barges to be transported to the installation site or may be towed while floating to the desired site. At the installation site the offshore platform is positioned on the sea bottom by the controlled flooding of the jacket legs and, possibly, pile sleeves.
In some instances it is desirable to preinstall the piles which are used to anchor the offshore platform to the floor of the body of water in the jacket legs and pile sleeves before the platform is transported to the installation site. When the piles are pre-installed in the jacket legs or pile sleeves, they must also be sealed against water leakage thereinto.
Various types of prior art plugs which are usable to seal the jacket legs, pile sleeves and conductor pipes of offshore platforms are illustrated in U.S. Pat. Nos. 3,434,293; 3,577,737; 4,142,371; 4,160,612; 4,178,967; 4,184,515; 4,215,951; 4,249,576; 4,262,702; 4,286,629; 4,292,004; 4,412,559; 4,421,138; 4,421,139; and 4,432,419.
Several of the prior art plugs use linkage mechanisms to control or facilitate the release of the locking members retaining the plugs in position within either the jacket leg, pile sleeve or conductor pipe. Examples of such prior art plugs using linkage mechanisms from the above group of prior art plugs are illustrated in U.S. Pat. Nos. 3,577,737; 4,160,612; 4,178,967; 4,215,951; 4,292,004; 4,412,559; 4,421,138; 4,421,139; and 4,432,419.
Other prior art plugs use shear pin arrangements to control or facilitate the release of the plugs or locking members retaining the plugs in position within either the jacket leg, pile sleeve or conductor pipe. Examples of such prior art plugs using shear pin arrangements are illustrated in U.S. Pat. Nos. 3,434,293; 4,184,515; 4,249,576; 4,262,702; and 4,286,629.
However, when linkage mechanisms are used to control or facilitate the release of the locking members retaining the plugs in position, to accomodate the variations in the roundness of the members in which they are installed the linkages must either be adjustable or be manufactured for specific plugs to be used in specific members.
Also, when shear pin arrangements are used to control or facilitate the release of the plugs or locking members, it is desirable to have the shear pins shear when desired and at a reasonable level of loading. This is not always possible since large diameter plugs and/or plugs used to withstand large pressure differentials thereacross may require large diameter shear pins having high shear loading levels.
It is also desirable to have a plug which will withstand pressure loadings from either direction thereacross, which may be easily installed in a member in which it is to be used, and which may be removed without requiring the running of permanently installed lines to the surface of the offshore platform.